1. Field of Invention
The present invention relates generally to loading/unloading cryogenic fluids between a ship and storage tanks Specifically, the present invention provides a loading system that extends from a free end of a transfer pipeline to a ship manifold.
2. Description of the Related Art
Typical LNG terminals have storage tanks onshore and a transfer system extending from the storage tanks to a loading/unloading platform where a ship is docked. The loading platform is located on a coast, a river bank, or offshore. At most terminals the transfer pipelines are supported on trestles (i.e., above the sea level), and terminate at a loading header on a loading platform. Articulated loading arms extend from the loading header to a ship manifold for fluid transfer.
In these conventional systems, the transfer pipelines are fixed at the platform with expansion loops or bellows to accommodate temperature changes, and articulated loading arms accommodate ship motions. These conventional hard arms are made of rigid pipe and swivel joints. They are mounted on a supporting structure/ frame with balancing weight to extend arms toward a ship manifold as disclosed in U.S. Pat. No. 3,434,491 to Bily.
Some improvements have been developed for the hard arms. For example, U.S. Pat. No. 7,857,001 to Kristensen et al discloses a loading system with a spiral and rigid pipe attached to a boom with trolleys to compensate longitudinal movements. U.S. Pat. No. 8,176,938 to Queau and Maurel discloses a loading system with a movable supporting frame that allows end displacements of a transfer pipeline. U.S. Pat. No. 8,181,662 to Pollack et al discloses a loading system with a supporting metal shaft pivotable at its base. Regardless of these improvements, all the systems above have the followings in common: rigid pipes and a number of swivel joints, and a large supporting structure. These arms are not only costly, but also require maintenance with leakage potential from the swivel joints.
At a few terminals where LNG transfer pipelines are inside an underground tunnel, a vertical shaft is used at a loading station near the ship to host a rigid riser and support a loading header on the top. The rigid riser extends from the transfer line below to the loading header above. The same hard arms discussed above are then fluidly connected to the loading header. US2010/0287957 to Liu discloses a similar transfer system with a vertical shaft and a rigid riser inside. The difference is that the Liu's system allows end displacements of a transfer pipeline. However, stresses could develop at rigid riser ends under thermal expansion/contraction of the subsea transfer pipeline.
Flexible hoses for cryogenic fluids have been developed. These cryogenic hoses typically consist of multiple layers of polyester fabric and polymeric film as well as inner and outer spiral wound stainless steel wires as disclosed in U.S. Pat. No. 4,417,603 to Argy. Flexible hoses have been disclosed as loading arms for example in U.S. Pat. No. 8,286,678 to Adkins et al, and used for ship to ship transfer of cryogenic fluids by Excelerate Energy.
For ship-to-shore transfer, several systems have been proposed using flexible hoses. U.S. Pat. No. 6,886,611 to Dupont and Paquet discloses a loading system between a LNG ship and a termination point of a transfer pipeline that is fixed on a gantry above a main platform. The loading system comprises flexible loading arm(s) with one end permanently hung at the termination point and a free end hung under another gantry with a winch and cable near a LNG ship. During a loading operation, a connection module is lifted over with a crane and tied in with a ship manifold (first connection). The free end of the flexible arm is then pulled over with another winch and cable, and fluidly connected with the connection module (second connection). This system avoids swivel joints, and provides a mean to break a free fall of the flexible arm in case of emergency. However, the system cannot accommodate end displacements of a transfer pipeline. Moreover, the system doubles the number of flange connection/disconnection for each loading arm that is time-consuming.
U.S. Pat. No. 7,299,835 to Dupont et al discloses a flexible loading system comprising flexible hoses with one end hung at a reel attached to a station and another end extended to a ship manifold. The flexible hoses can be stored by rotating the reel after loading operations. Again, swivel joints are needed at the reel axis or at the rotatable connection.
A single point mooring system has also been proposed for subsea LNG transfer. The system comprises a cryogenic riser connecting subsea pipelines and a turret or the like, and loading arm(s) extended from the turret to a LNG ship. For example, U.S. Pat. No. 7,438,617 to Poldervaart et al discloses a system comprising a floating buoy, turntable reel as well as rotatable connection between flexible hoses and transfer risers. U.S. Pat. No. 7,836,840 to Ehrhardt et al discloses a system comprising a floating buoy, a flexible riser and a flexible arm with a submersible turret (i.e., rotatable) connection between the flexible arm end and socket at the ship bottom.
Other systems have a vertical post anchored at the seabed. U.S. Pat. No. 3,379,027 to Mowell discloses a fixed tower, a rigid riser, a rigid loading arm partially submerged in water. U.S. Pat. No. 7,147,021 to Dupont and Paquet discloses a system that has a riser attached to a vertical post with a rotatable connection, and piping along the boom that extends from the riser to a LNG ship. EP 1462358 to De Baan uses a vertical post as a riser, and flexible arms extend from the riser top to a ship for fluid transfer.
The drawback of these systems is the need for rotatable connection at an end of a loading arm as well as the difficulty to access underwater components.
In summary, there is a need to develop a loading system that not only allows end displacements of a transfer pipeline, but also overcomes the drawbacks discussed above.